Gas exchange rates and chlorophyll content of epi- and endolithic lichens from the Trieste Karst (NE Italy)

The photosynthetic activity of calcicolous endo- and epilithic lichens from the Trieste Karst area (NE Italy) was investigated. The data consist of: (a) gas exchange rates of Acrocordia conoidea, Petractis clausa, Rinodina immersa (endolithic), and Aspicilia calcarea (epilithic), recorded at different combinations of temperature, water content and radiation flux values, (b) chlorophyll content values of nine species, and (c)δ¹³ C values measured in 24 lichen species with different growth-forms. The results show that: (1) the maximum photosynthetic rates of endolithic lichens are rather small, ranging between 0·2 and 1·5μmol CO₂ m^-2 h^-1 at optimal conditions; (2) the relation between thallus water content and photosynthesis differs from that of foliose and fruticose lichens; the optimum water content of endolithic lichens is particularly small, when expressed in g H₂ O cm^-2 ; (3) the algae of endolithic lichens, which belong to different systematic groups, are light-saturated at a small radiation flux; (4) chlorophyll contents of endolithic lichens are rather large, being similar to those of some parmelioid lichens. The ecological implications of the endolithic growth-form are briefly discussed. Endolithic lichens should be regarded as slow-growing, stress-tolerant organisms, which are rather similar in their physiology to epilithic crustose lichens; they have a high resistance to CO₂ diffusion, saturation being reached only at a very large CO₂ concentration.